package com.headStorm.forkAndJoin;

import com.headStorm.factory.Main;

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;

/**
 * fork join 框架出现的意义是将一个大的任务切割成若干个
 * 互不影响的小任务进行执行
 */
public class CountTask extends RecursiveTask<Integer> {

    private static final int THRESHOLD = 2; //阀值

    private int start;
    private int end;

    public CountTask(int start , int end){
        this.start = start;
        this.end = end;
    }

    @Override
    protected Integer compute() {
        int sum  = 0;
        boolean canCompute = (end - start) <= THRESHOLD;
        if(canCompute){
            for (int i = start; i <= end ; i++){
                sum += 1;
            }
        }else{
            //如果任务大于阀值,就分裂成两个子任务进行计算
            int middle = (start + end)/2;
            CountTask leftTask = new CountTask(start,middle);
            CountTask rightTask = new CountTask(middle+1 , end);

            //执行子任务
            leftTask.fork();
            rightTask.fork();

            //等待子任务执行完之后，并且得到结果
            int leftResult = leftTask.join();
            int rightResult = rightTask.join();
            //合并子任务
            sum = leftResult + rightResult;
        }
        return sum;
    }

    public static void main(String[] args) {
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        //生成一个计算任务,负责计算 1+2+3+4
        CountTask countTask = new CountTask(1,4);
        //执行一个任务
        Future<Integer> result = forkJoinPool.submit(countTask);
        try {
            System.out.println(result.get());
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}
